Populations of the order of bark beetles, Pityogenes chalcographus [L.] infest Norway spruce, Picea abies [L.], recently creating a serious pest problem in European spruce stands. These beetles aggregate like other species of Pityogenes on standing trees or slash of freshly cut trees, in response to a pheromone released by the host-selecting male beetles. It is the object of the present invention to provide compositions containing a compound which causes the populations of Pityogenes chalcographus to aggregate in order to facilitate selective trapping.